1. Field of the Invention
The present invention relates to a plasma processing apparatus, a plasma processing method, and a storage medium, and in particular relates to a plasma processing apparatus having an electrode that is electrically insulated from other component elements.
2. Description of the Related Art
Parallel plate type plasma processing apparatuses are known that have a substrate processing chamber that has therein a processing space into which is transferred a wafer as a substrate, a lower electrode that is disposed in the substrate processing chamber and is connected to a radio frequency power source, and an upper electrode that is disposed such as to face the lower electrode. In such a plasma processing apparatus, a processing gas is introduced into the processing space, and radio frequency electrical power is applied into the processing space between the upper electrode and the lower electrode. When a wafer has been transferred into the processing space and mounted on the lower electrode, the introduced processing gas is turned into plasma through the radio frequency electrical power so as to produce ions and so on, and the wafer is subjected to plasma processing, for example etching processing, by the ions and so on.
In the case of forming the plasma by introducing a CF type processing gas into the processing space as the processing gas, a CF type reaction product is produced in the processing space, and becomes attached as polymer to a surface of each of the upper electrode and the lower electrode, and an inner wall surface of the substrate processing chamber. Here, because radio frequency electrical power is supplied to each of the upper electrode and the lower electrode, a potential on the surface of each of the upper electrode and the lower electrode fluctuates, and hence a potential difference arises between the plasma in the processing space and the surface of each of the upper electrode and the lower electrode. Ions collide with the surface of each of the upper electrode and the lower electrode in accordance with the potential difference, whereby the polymer attached to the surface is removed. Moreover, the wall of the substrate processing chamber is generally grounded, and hence a potential difference arises between the plasma in the processing space and the inner wall surface of the substrate processing chamber. Polymer attached to the inner wall surface is thus also removed through collisions with ions.
There is also known a plasma processing apparatus in which a dust-collecting electrode is disposed in the processing space so as to reliably prevent polymer from becoming attached to the surface of each of the upper electrode and the lower electrode, and the inner wall surface of the substrate processing chamber. In such a plasma processing apparatus, a DC voltage is applied to the dust-collecting electrode, whereby the dust-collecting electrode electrostatically attracts and thus captures reaction product in the processing space (see, for example, Japanese Laid-open Patent Publication (Kokai) No. H07-106307).
Moreover, in recent years, as semiconductor devices have become increasingly highly integrated, patterns formed on wafers have been made finer. Such making semiconductor devices finer is achieved by reducing the light source wavelength of an exposing apparatus used in photolithography, and at present it has come to be that an argon fluoride (ArF) excimer laser of wavelength 0.193 μm is used as the light source.
For a photoresist film (ArF resist film) used in photolithography using such an ArF excimer laser, the etching selectivity thereof relative to a semiconductor device constituent material is insufficient, and hence it is difficult to etch the constituent material accurately using a single layer of such an ArF resist film as a mask.
Moreover, as patterns are made finer, it becomes impossible to make the photoresist film thick. It is thus difficult to achieve the high etching selectivity required of the photoresist film relative to the semiconductor device constituent material.
As an example of a process for solving such problems, multi-layer resist processes have thus been developed. A multi-layer resist process is a process in which, to improve the functioning as a mask material in etching of the constituent material, the resist is made to be multi-layer, whereby the target layer can be precisely processed.
Such a multi-layer resist process is described, for example, in Japanese Laid-open Patent Publication (Kokai) No. 2002-093778. Following is a brief description of the multi-layer resist process described in Japanese Laid-open Patent Publication (Kokai) No. 2002-093778.
First, on a semiconductor device constituent material (a silicon oxide film type insulating film, e.g. SiO2), there are formed in order a lower layer resist film (a coating type carbon film, e.g. amorphous carbon) that can be selectively etched relative to the constituent material, an oxide film (SOG film, e.g. SiO2 or SiOC) that can be selectively etched relative to the lower layer resist film, and a photoresist film.
Next, the photoresist film is patterned by photolithography, and the oxide film (inorganic film) is etched using the photoresist film as a mask, thus transferring the pattern of the photoresist film onto the oxide film. Next, the lower layer resist film (organic film) is etched using the patterned oxide film as a mask, thus transferring the pattern of the oxide film onto the lower layer resist film. Processing of the constituent material (inorganic film) is then carried out using the lower layer resist film as a mask.
Here, in an etching apparatus for the insulating film, from the viewpoint of improving efficiency, it is required that both the inorganic film etching of the silicon oxide film type insulating film which is made of a silicon-based material such as SiO2, and the organic film etching of the coating type carbon film which is made of a carbon-based material such as amorphous carbon be carried out in the same chamber. In the etching of the SiO2 material, a CF type gas such as C4F8 is mainly used, and to achieve a high etching rate, an etching apparatus that enables high-electron-density high-bias etching to be achieved is required. On the other hand, in the organic film etching, a gas not containing F such as O2, CO, N2, or H2 is used, and an etching apparatus that enables high-electron-density low-bias etching to be achieved is required.
Meanwhile, in recent years, so that the plasma in the processing space can be controlled to be in a desired state, plasma processing apparatuses in which radio frequency electrical power is not supplied to the upper electrode have been developed. In such a plasma processing apparatus, the upper electrode is electrically insulated from the wall of the substrate processing chamber, and hence the radio frequency electrical power supplied to the lower electrode is not supplied into the upper electrode via the wall, which is grounded. Moreover, the upper electrode receives charge from the plasma, but there is no outflow of the charge from the upper electrode, and hence the upper electrode is charged up, whereby a potential difference between a surface of the upper electrode and the plasma in the processing space is reduced. The energy of ions colliding with the surface of the upper electrode is thus reduced, and hence polymer that has become attached to the surface of the upper electrode cannot be removed.
In the case that the polymer attached to the surface of the upper electrode is not removed, problems arise, for example the polymer detaches to form particles, which become attached to the front surface of wafers, causing a worsening of the yield of semiconductor devices manufactured from the wafers.
Moreover, in the case of using, as an etching apparatus that carries out a multi-layer resist process as described above, an apparatus that has a silicon-based upper electrode and in which radio frequency electrical power is applied into the processing space from each of the upper electrode and the lower electrode, it is known that if the silicon-based upper electrode is sputtered in the inorganic film processing, then even if high-electron-density plasma is used, a high selectivity relative to the photoresist acting as the mask film can be achieved. However, in the organic film processing, a problem arises that, upon radio frequency electrical power being applied to the upper electrode, the silicon-based upper electrode material flies off due to sputtering and accumulates on the wafer. Because the processing gas supplied into the processing space in the organic film processing is a gas not containing F, the silicon-based material accumulated on the wafer cannot be removed, but rather accumulates as residue.
In the case that an apparatus in which radio frequency electrical power is applied from only the lower electrode is used, the above problem does not arise. However, in the inorganic film processing, because the effect of the silicon-based upper electrode being sputtered is not obtained, in the case that high-electron-density plasma is used, a problem of the photoresist selectivity decreasing arises.